add fish completions

[fbehrens]

Hi @steipete, i work with fish shell and have created those completions from summarize --help with claude code.

If you merge it i will sent a pr to the homebrew-tap to make it just work in fish shell.

[steipete]

Landed via temp rebase onto main.

• Gate: pnpm -s build && pnpm -s lint && pnpm -s test
• Land commit: 57f5436
• Merge commit: ba0a6d6

Thanks @fbehrens!

[fbehrens]

Thanks for merging,
Those were just prompted to create from the --help output.
May look into make this more reliable,